1. Field of the Invention
This invention relates to a drill bit for drilling blind holes to a selected depth and especially relates to accessories providing depth choices to the drill operator for each drill bit of a desired diameter.
2. Review of the Prior Art
When drilling blind holes into wood, plywood, flakeboard, particle board, hardboard, and composite materials such as veneered wood and wood bonded to materials such as "FORMICA", a trademark of the Formica Corporation, 155 Rte. 46W, CN 980, Wayne, N.J. 07474, for various high-pressure laminated plastic sheets of melamine and phenolic materials used especially as decorative laminates and for chemical and heat-resistant surfaces, it can be very difficult to avoid doing irreparable damage by drilling the blind hole mere fractions of an inch too deeply. When drilling holes into wall panelling behind which pipes or electric wires may lie, it is also important to keep the hole as dependably shallow as possible. Further, when drilling holes into automobile body panels behind which electrical wires, control cables, and the like may lie, it is essential that the drill bit dependably penetrate very little more than the thickness of the metal.
U.S. Pat. No. 3,552,503 describes a clean-out drill for drilling and cleaning out the dust-like residue of drilling blind holes in concrete. The drill comprises the combination of a drill shank having helical relief flutes with a reduced-diameter cutting section and a terminal section of selected diameter and length providing a shoulder spaced from the cutting tip, and with a simple washer fitted over the reduced-section drill shank and welded to the abutment lands between the relief flutes on the drill shank. The circular hole of the washer cooperates with the relief flutes to provide discharge passageways through which the residue of drilling is moved from one side to the other side of the washer for effecting discharge by centrifugal force laterally of the blind hole.
U.S. Pat. No. 4,993,894 describes a drill for drilling holes in masonry and comprises a depth stop mounted on the drill shank and formed as a resilient anti-vibration element in order to avoid damage to the masonry surface. The depth stop is formed of polyurethane or a similar plastic material. During swiveling movement while undercutting the drilled hole, the contact face of the depth stop lying against the wall surface does not change its position so that the wall surface not only sustains no damage, but also the optimum contact area of the depth stop with the wall surface is maintained while reaming out the undercut.
An adjustable drill stop set, advertised in a 1985 catalog of Sporty's Tool Shop, comprises stops for drill sizes 1/8 inch through 1/2 inch in 1/16 increments which are slipped over a drill bit to a measured depth and secured by tightening an Allen head locking screw which is mounted in the stop.
A plastic depth gauge, which locks to the shaft of a drill bit at any required distance to limit the depth of a hole, is described in an article entitled "Electric drills" and subtitled "The 1/2-inch drill".
A screw drill and plug mate, made by Great Neck Saw Mfrs., Inc., Dept HA, Mineola, N.Y., is described in Hardware Age, May 17, 1962. The "screw drill is adjustable to any length of wood screw. It drills a precision hole for screw body, countersinks, counterbores, and automatically stops at pre-set depth. Drills the correct diameter for woodscrews 5-to-14, counterbores for flat head screws, putty or wood plug."
The Century Drill Stop, made by Century Drill & Tool Co., 322 South Green, Chicago, Ill. 60607 and advertised on page 143 of the December 1969 issue of Hardware Age, fits over a drill bit, has a knurled top, threads therebeneath, and a knurled lower part which apparently allows setting at a desired distance from the tip of the bit to make holes having a uniform depth.
An advertisement labelled "MASTER MECHANIC" for a "5-Pc. Cordless Drill Bit Set" has been noted as a True Value.sup.R savings coupon.
These drill stops have various disadvantages, such as limited adjustability or requiring use of set screws. A drill stop which is a part of a drill bit and also has a simply operable depth adjusting means is needed.